Guardian 4721, Repair Manual

Page: 17 / 115

GENERAL INFORMATION
SECTION 1.5
ENGINE-GENERATOR PROTECTIVE DEVICES
PART 1
Page 13
GENERAL
Standby electric power generators will often run unat-
tended for long periods of time. Such operating para-
meters as (a) engine oil pressure, (b) engine temper-
ature, (c) engine operating speed, and (d) engine
cranking and startup are not monitored by an operator
during automatic operation. Because engine opera-
tion will not be monitored, the use of engine protective
safety devices is required to prevent engine damage
in the event of a problem.
Prepackaged generator engines mount several engine
protective devices. These devices work in conjunction
with a control circuit board, to protect the engine
against such operating faults as (a) low engine oil
pressure, (b) high temperature, (c) overspeed, and (d)
overcrank. On occurrence of any one or more of those
operating faults, control board action will effect an
engine shutdown.
LOW OIL PRESSURE SHUTDOWN:
See Figure 1. Prepackaged generators with liquid
cooled engine are equipped with an oil pressure
switch having a closing pressure of about 10 psi.
Should oil pressure drop below that value, an auto-
matic engine shutdown will occur. Circuit operation is
similar to that of air-cooled units.
LOW COOLANT
LEVEL SWITCH
LOW OIL
PRESSURE
SWITCH
HIGH COOLANT
TEMPERATURE
SWITCH
OVERCRANK AND OVERSPEED
SHUTDOWN ARE CONTROLLED
BY THE CIRCUIT BOARD
Figure 1. Protective Devices on Liquid Cooled Engine